The long term evolution (Long Term Evolution, LTE) R8 protocol and subsequent versions define a basic feedback mode for optimizing transmission efficiency, especially for downlink transmission, where scheduling is performed in a radio resource management (Radio Resource Management, RRM) entity according to a frequency selectivity characteristic, including modulation and coding scheme (Modulation and Coding Scheme, MCS) selection, multiple-input multiple-output (Multiple-Input Multiple-Output, MIMO) mode selection, user selection, and the like. In a heterogeneous network (Heterogeneous Network, HetNet), because interference comes from multiple interference sources such as a local macro cell, a neighboring macro cell, and other micro cells, the interference itself cannot be simply deemed as white Gaussian noise. Therefore, a feedback mechanism needs to be improved so that the interference includes, to the greatest extent, only interference information from a macro cell, thereby effectively improving the performance of the micro cell. Correspondingly, in the protocol, multiple base stations in cooperation need to be explicitly notified of an interference condition, so as to coordinate a corresponding radio resource. Because the coordination is required only for a small part of micro cells in the HetNet, it is easy for implementation. Definitely, coordination in a larger range is not excluded.
After a micro cell (including a Picocell, a Femtocell, and the like) is introduced into a macro cell, cell density is increased, which may effectively improve the coverage and increase the system capacity. Generally, in order to use a frequency resource effectively, the same frequency is used in the same macro cell. However, in this case, interference of a neighboring cell is increased naturally. As regards how to solve this problem, Table 1 shows transmit power corresponding to different types of cells.
TABLE 1Cell TypeTransmit Power [dBm]Macro cell43Micro cell30Picocell23-30Femtocell<23 
FIG. 1 is a distribution diagram of a signal to interference plus noise ratio (Signal to Interference plus Noise Ratio, SINR) of a typical downlink HetNet network. The HetNet is formed by a macro base station and a micro base station, where the micro base station may be a Pico base station, a Femtocell base station, or a relay. The micro base station has small transmit power, and therefore, may be deployed more easily than the macro base station. Generally, a frequency reuse factor of an LTE system is 1, indicating that all neighboring cells transmit a signal over the same frequency resource. As a result, some macro cells receive serious interference from a neighboring macro base station or micro base station, and some micro cells receive serious interference from a macro base station that covers the micro cells. Therefore, a performance trade-off must be performed in the HetNet network.
The LTE R8 protocol defines a feedback mechanism between an eNodeB base station and a user equipment. Information exchanged between an LTE base station and a UE includes:
1. channel quality information (Channel Quality Indicator, CQI): indicating an optimal MCS;
2. a preferred matrix index (Preferred Matrix Index, PMI): indicating a preferred precoding matrix; and
3. a rank indicator (Rank Indicator, RI): indicating a rank that may be transmitted in a preferred MIMO mode.
Feedback information may be sent periodically or non-periodically, and the feedback may be full-band feedback or sub-band feedback. The feedback may use a differential mode, thereby combining full-band and sub-band characteristics, and feeding back as much information as possible without reducing feedback accuracy or with a small reduction. The protocol specifies no pilot for measuring interference. Therefore, an interference signal cannot be merely simplified into Gaussian noise. In the prior art, interference is determined mainly by using the following methods:
1. using the number of antennas or using polarization;
2. using a MIMO transmission mode, for example, space division multiple access (Space Division Multiple Access, SDMA), single user multiplexing, and the like;
3. using a downtilt angle of an antenna; and
4. using transmit power.
Based on information fed back by a UE, an RRM scheduler allocates time/frequency/space resources to a group of users. Each base station schedules a user thereof based on a scheduling policy of the base station. In the existing protocol, no scheduling information is exchanged between base stations, especially, for example, between base stations on different levels in a HetNet scenario.
In this scheduling mode, because no user scheduling information is exchanged between base stations, an interference condition after the scheduling cannot be predicted, which easily leads to a phenomenon of resource “collision”. For example, base stations schedule a high MCS or high power on the same resource, resulting in very large interference between cells, which reduces throughput of the whole mobile communication system.